The invention relates to desiccant containers for any purpose. However, specific embodiments will be described with respect to desiccant containers within HVAC systems.
A typical vehicle air conditioning system, for example, incorporates a compressor, a condenser, an expansion device, an evaporator and a refrigerant storage device. The compressor compresses refrigerant. The refrigerant flows to the condenser, where it changes state from gas to liquid. In a system with a thermal expansion valve (a “TXV system”), refrigerant then passes into a refrigerant storage device called a receiver/dryer (R/D) before passing to the expansion device. In a system with a fixed orifice tube (an “FOT system”), refrigerant then passes directly from the condenser to the expansion device. The expansion device is used to significantly lower the pressure and temperature of the refrigerant before it passes to the evaporator. After the expansion device, the liquid refrigerant then flows to the evaporator. At that stage, an air blower passes air over the evaporator to the passenger compartment of the vehicle, thereby cooling the air within the vehicle. The heat transfer from the ambient air to the evaporator causes most of the refrigerant to change from a liquid to a gas.
In an FOT system, the refrigerant (now mostly gas and some liquid) flows from the evaporator to a refrigerant storage device called an accumulator. (In a TXV system, the refrigerant flows from the evaporator to the compressor directly.)
One purpose of the accumulator is to separate liquid refrigerant from gaseous refrigerant, so that only gaseous refrigerant returns to the compressor. Liquid refrigerant entering the compressor causes “flooding” which in turn reduces system efficiency and can damage the compressor. Hence it is standard practice to include an accumulator between the evaporator and the compressor to separate and store the excess or residual liquid. The residual liquid refrigerant in the accumulator eventually turns to a gaseous state and is then passed to the compressor.
Accumulators and receivers/dryers often incorporate a desiccant to prevent (or at least limit) moisture ingression in the compressor and the resulting damage or loss of efficiency to the air conditioning system. (For simplicity, hereinafter, the term “accumulator” or “refrigerant storage device” will refer to both accumulators and receiver/dryers.)
Particulate desiccants are often used in such systems because of the high area-to-volume ratios of the particles with respect to the surrounding air or fluid. Because the desiccant particles must be held in the air or fluid stream and prevented from contaminating other parts of the air conditioning system, the particles must be held in a container which is permeable to the air or fluid but impermeable to the particles.
In some known cases, loose desiccant is contained within a bag, the bag being constrained between filters. The filters are often discs made of felt, gauze, fiber or plastic (fused). Such bags are problematic because they can be easily damaged during assembly and/or testing. A tear in the bag allows the loose desiccant particles to escape and potentially enter the air-conditioning system, where they can damage the accumulator and other components.
In certain other systems, it is known to confine the desiccant within a hard container. In those cases, filter discs, such as those described above, are typically placed in the top and bottom of the desiccant container during manufacturing. However, there are certain drawbacks associated with the use of such filter discs. For example, the materials used within the filter discs, such as polyester or polypropylene matted or needles felt, for example, have been known to stimulate a reaction with the air conditioning refrigerant R-134A to create a significant noise within the air conditioning system. It would be desirable to eliminate the noise. It would also be desirable to eliminate the cost associated with the purchase of the filter discs. It would also be desirable to eliminate the time and cost associated with their installation within the desiccant cup. It would also be desirable to eliminate filter discs because they deteriorate during service and release high aspect ratio fibres into the air conditioning system.
A number of desiccant cups are known which have a one-piece cup with a one-piece cap, such as that taught in U.S. Pat. No. 5,522,204 in the name of Wood. The cup taught in Wood incorporates holes formed within the cap and cup bottom. However, such cups require additional filter layers placed against the cap and cup bottom. As well, holes formed within the cap and cup bottom in this manner have a number of drawbacks. One drawback is that diameter of the holes is large enough to allow desiccant particles to pass through or become caught or blocked in the holes. Therefore, such cups require a separate filter. As well, it would be desirable to have a more open area for fluid to pass through than is permitted through an array of holes, such as taught in Wood, because more open area reduces pressure drop in the system, thereby increasing efficiency.